The typical optical display assembly contains a light source that is required to observe the information presented by the display. In battery powered equipment like laptop computers, the light source can represent a substantial fraction of the total power draw of the equipment. Therefore, reducing the amount of power required to produce a given luminance, increases battery life which is especially desirable in battery powered equipment.
The 3M brand Brightness Enhancement Film available from the 3M Company of Maplewood, Minn., USA, is used to address this problem. This material is a film that includes a periodic array of prisms. The prisms are large in comparison with the wavelength of light. This material collects light from "off-axis" and redirects or "recycles" this light "on-axis" toward the viewer. In use, this material increases the on-axis luminance at the expense of off-axis luminance. In this fashion, the material can help the display designer achieve the desired amount of on-axis luminance with reduced power consumption.
However, with this product there is a sharp decline in luminance as one views the optical display assembly off-axis. The sharp reduction in luminance for an off-axis observer has proved to be undesirable in some applications.
Another problem associated with the use of periodic films in optical display assemblies is the generation of moire patterns that are visible to the viewer and are distracting and undesirable.